Thermal management systems and methods for wafer processing systems

ABSTRACT

A workpiece holder includes a puck having a cylindrical axis, a radius about the cylindrical axis, and a thickness. At least a top surface of the puck is substantially planar, and the puck defines one or more thermal breaks. Each thermal break is a radial recess that intersects at least one of the top surface and a bottom surface of the cylindrical puck. The radial recess has a thermal break depth that extends through at least half of the puck thickness, and a thermal break radius that is at least one-half of the puck radius. A method of processing a wafer includes processing the wafer with a first process that provides a first center-to-edge process variation, and subsequently, processing the wafer with a second process that provides a second center-to-edge process variation that substantially compensates for the first center-to-edge process variation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure is related to the subject matter ofcommonly-owned U.S. patent application Ser. No. 14/820,422, being filedconcurrently with this application on Aug. 6, 2015, and incorporatedherein by reference in its entirety for all purposes.

TECHNICAL FIELD

The present disclosure applies broadly to the field of processingequipment. More specifically, systems and methods for providingspatially tailored processing of a workpiece are disclosed.

BACKGROUND

Integrated circuits and other semiconductor products are oftenfabricated on surfaces of substrates called “wafers.” Sometimesprocessing is performed on groups of wafers held in a carrier, whileother times processing and testing are performed on one wafer at a time.When single wafer processing or testing is performed, the wafer may bepositioned on a wafer chuck. Other workpieces may also be processed onsimilar chucks. Chucks can be temperature controlled in order to controltemperature of a workpiece for processing.

SUMMARY

In an embodiment, a workpiece holder positions a workpiece forprocessing. The workpiece holder includes a substantially cylindricalpuck that is characterized by a cylindrical axis, a puck radius aboutthe cylindrical axis, and a puck thickness. The puck radius is at leastfour times the puck thickness, at least a top surface of the cylindricalpuck is substantially planar, and the cylindrical puck defines one ormore radial thermal breaks. Each thermal break is characterized as aradial recess that intersects at least one of the top surface and abottom surface of the cylindrical puck. The radial recess ischaracterized by a thermal break depth that extends from the top surfaceor the bottom surface of the puck through at least half of the puckthickness, and a thermal break radius that is disposed symmetricallyabout the cylindrical axis, and is at least one-half of the puck radius.

In an embodiment, a method of processing a wafer includes processing thewafer with a first process that provides a first center-to-edge processvariation; and subsequently, processing the wafer with a second processthat provides a second center-to-edge process variation. The secondcenter-to-edge process variation substantially compensates for the firstcenter-to-edge process variation.

In an embodiment, a workpiece holder that positions a workpiece forprocessing. The workpiece holder includes a substantially cylindricalpuck that is characterized by a cylindrical axis and a substantiallyplanar top surface. The cylindrical puck defines two radial thermalbreaks. A first one of the thermal breaks is characterized as a radialrecess that intersects a bottom surface of the cylindrical puck at afirst radius, and extends from the bottom surface through at leastone-half of a thickness of the puck. A second one of the thermal breaksis characterized as a radial recess that intersects the top surface at asecond radius that is greater than the first radius, and extends fromthe top surface through at least one-half of the thickness of the puck.A thermal sink extends substantially beneath the bottom surface of thepuck, and includes a metal plate that flows a heat exchange fluidthrough channels defined therein, to maintain a reference temperaturefor the puck. A first heating device is disposed between the thermalsink and the puck. The first heating device is in thermal communicationwith the bottom surface of the puck and with the thermal sink, withinthe first radius. A second heating device is disposed between thethermal sink and the puck. The second heating device is in thermalcommunication with the bottom surface of the puck and with the thermalsink, outside the second radius.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates major elements of a processing systemhaving a workpiece holder, according to an embodiment.

FIG. 2 is a schematic cross sectional diagram illustrating exemplaryconstruction details of the workpiece holder of FIG. 1.

FIG. 3 is a schematic cross sectional diagram illustrating applicationof heaters and a thermal sink to inner and outer portions of a puck thatforms part of the workpiece holder of FIG. 1, in accord with anembodiment.

FIG. 4 is a schematic cross-sectional view that illustrates features ofa puck, a resistive heater, and a thermal sink, in accord with anembodiment.

FIG. 5 schematically illustrates a layout of heater trace within theinner resistive heater of FIG. 4, in accord with an embodiment.

FIG. 6 schematically illustrates a lift pin mechanism disposed within athermal break, in accord with an embodiment.

FIG. 7 schematically illustrates, in a plan view, a three lift pinarrangement where lift pins are disposed within a thermal break, inaccord with an embodiment.

FIG. 8 is a flowchart of a method for processing a wafer or otherworkpiece, in accord with an embodiment.

FIG. 9 is a flowchart of a method that includes, but is not limited to,one step of the method of FIG. 8.

FIG. 10 is a flowchart of a method that includes, but is not limited to,another step of the method of FIG. 8.

DETAILED DESCRIPTION

The present disclosure may be understood by reference to the followingdetailed description taken in conjunction with the drawings describedbelow, wherein like reference numerals are used throughout the severaldrawings to refer to similar components. It is noted that, for purposesof illustrative clarity, certain elements in the drawings may not bedrawn to scale. Specific instances of an item may be referred to by useof a numeral following a dash (e.g., heaters 220-1, 220-2) whilenumerals without parentheses refer to any such item (e.g., heaters 220).In instances where multiple instances of an item are shown, only some ofthe instances may be labeled, for clarity of illustration.

FIG. 1 schematically illustrates major elements of a wafer processingsystem 100. System 100 is depicted as a single wafer, semiconductorwafer plasma processing system, but it will be apparent to one skilledin the art that the techniques and principles herein are applicable towafer processing systems of any type (e.g., systems that do notnecessarily process wafers or semiconductors, and do not necessarilyutilize plasmas for the processing). Processing system 100 includes ahousing 110 for a wafer interface 115, a user interface 120, a plasmaprocessing unit 130, a controller 140 and one or more power supplies150. Processing system 100 is supported by various utilities that mayinclude gas(es) 155, external power 170, vacuum 160 and optionallyothers. Internal plumbing and electrical connections within processingsystem 100 are not shown, for clarity of illustration.

Processing system 100 is shown as a so-called indirect plasma processingsystem that generates a plasma in a first location and directs theplasma and/or plasma products (e.g., ions, molecular fragments,energized species and the like) to a second location where processingoccurs. Thus, in FIG. 1, plasma processing unit 130 includes a plasmasource 132 that supplies plasma and/or plasma products for a processchamber 134. Process chamber 134 includes one or more workpiece holders135, upon which wafer interface 115 places a workpiece 50 (e.g., asemiconductor wafer, but could be a different type of workpiece) to beheld for processing. When workpiece 50 is a semiconductor wafer,workpiece holder 135 is often referred to as a wafer chuck. Inoperation, gas(es) 155 are introduced into plasma source 132 and a radiofrequency generator (RF Gen) 165 supplies power to ignite a plasmawithin plasma source 132. Plasma and/or plasma products pass from plasmasource 132 through a diffuser plate 137 to process chamber 134, whereworkpiece 50 is processed. Alternatively or in addition to plasma fromplasma source 132, a plasma may also be ignited within process chamber134 for direct plasma processing of workpiece 50.

Embodiments herein provide new and useful functionality for waferprocessing systems. Semiconductor wafer sizes have increased whilefeature sizes have decreased significantly over the years, so that moreintegrated circuits with greater functionality can be harvested perwafer processed. Processing smaller features while wafers grow largerrequires significant improvements in processing uniformity. Becausechemical reaction rates are often temperature sensitive, temperaturecontrol across wafers during processing is often key to uniformprocessing.

Also, some types of processing can have radial effects (e.g., processingthat varies from center to edge of a wafer). Some types of processequipment control these effects better than others, that is, someachieve high radial process uniformity while others do not. Embodimentsherein recognize that not only are radial effects important to control,but it would be further advantageous to be able to provide radialprocessing control that can be tailored to compensate for processingthat cannot achieve such control. For example, consider a case in whicha layer is deposited on a wafer and then selectively etched off, as iscommon in semiconductor processing. If the deposition step is known todeposit a thicker layer at the wafer's edge than at its center, acompensating etch step would advantageously provide a higher etch rateat the wafer's edge than at its center, so that the deposited layerwould be etched to completion at all parts of the wafer at the sametime. Similarly, if an etch process were known to have a center-to-edgevariation, a compensating deposition preceding the etch process could beadjusted to provide a corresponding variation.

In many such cases of processing with radial effects, a compensatingprocess can be provided by providing explicit center-to-edge temperaturevariation, because temperature often substantially influences reactionrates of processes.

FIG. 2 is a schematic cross section that illustrates exemplaryconstruction details of workpiece holder 135, FIG. 1. As shown in FIG.2, workpiece holder 135 includes a puck 200 that is substantiallycylindrical, and is characterized in terms of having a puck radius r1 ina radial direction R from a cylindrical axis Z. In use, a workpiece 50(e.g., a wafer) may be placed on puck 200 for processing. A bottomsurface 204 of puck 200 is taken to be a median bottom surface height ofpuck 200; that is, a plane that defines the typical bottom surfaceheight of puck 200 in the direction of axis Z exclusive of features suchas edge rings or other protrusions 206, or indentations 208, that puck200 may form as attachment points for other hardware. Similarly, a topsurface 202 is taken to be a planar surface configured to accommodateworkpiece 50, irrespective of grooves that may be formed therein (e.g.,as vacuum channels, see FIG. 4) and/or other features that retainworkpiece 50. All such protrusions, indentations, grooves, rings and thelike do not, in the context of this specification, detract from thecharacterization of puck 200 as “substantially cylindrical.” Puck 200may also be characterized in terms of having a thickness t betweenbottom surface 204 and top surface 202, as shown. In certainembodiments, puck radius r1 is at least four times puck thickness t, butthis is not a requirement.

Puck 200 defines one or more radial thermal breaks 210, as shown.Thermal breaks 210 are radial recesses defined in puck 200, thatintersect at least one of top surface 202 or bottom surface 204 of puck200. Thermal breaks 210 act as the term implies, that is, they providethermal resistance, between a radially inner portion 212, and a radiallyouter portion 214, of puck 200. This facilitates explicit radial (e.g.,center-to-edge) thermal control of the radially inner and outer portionsof puck 200, which is advantageous in terms of either providing precisethermal matching of the inner and outer portions, or of providingdeliberate temperature variation across the inner and outer portions.Thermal breaks 210 can be characterized in terms of having a thermalbreak depth and a thermal break radius. Depth of thermal breaks 210 canvary among embodiments, but the thermal break depth usually exceedsone-half of thickness t. Radial positioning of thermal breaks 210 canalso vary among embodiments, but the thermal break radius r2 is usuallyat least one-half of puck radius r1, and in other embodiments r2 may bethree-fourths, four-fifths, five sixths or more of puck radius r1.Certain embodiments may use a single thermal break 210, while otherembodiments may use two thermal breaks 210 (as shown in FIG. 2) or more.A demarcation point between radially inner portion 212 and radiallyouter portion 214 is illustrated as a radially average position betweentwo thermal breaks 210, but in embodiments having a single thermal break210, such demarcation point can be considered to be the radial midpointof the single thermal break 210.

One way in which thermal breaks, as illustrated in FIG. 2, can be usedadvantageously is to provide radially applied heating and/or cooling toinner portion 212 and outer portion 214 of puck 200. FIG. 3 is aschematic cross sectional diagram illustrating application of heatersand a thermal sink to inner and outer portions of puck 200. Somemechanical details of puck 200 are not shown in FIG. 3, for clarity ofillustration. FIG. 3 illustrates a central channel 201 defined by puck200 and an optional thermal sink 230. Central channel 201 is describedin connection with FIG. 4. Inner heaters 220-1 and outer heaters 220-2are disposed against, and are in thermal communication with, puck 200.It may be advantageous for heaters 220 to be spread across largeportions of lower surface 204, but the distribution of heaters 220across surface 204 can vary in embodiments. Heat provided by heaters 220will substantially control the temperatures of inner portion 212 andouter portion 214 of puck 200; thermal breaks 210 assist in thermallyisolating portions 212 and 214 from one another, to improve theprecision of thermal control. Heaters 220 are typically resistiveheaters, but other types of heaters (e.g., utilizing forced gas orliquid) may be implemented.

Optional thermal sink 230 may also be provided. Thermal sink 230 may becontrolled to present a lower temperature than typical operatingtemperatures, for example by flowing a heat exchange fluid therethrough,or by using a cooling device such as a Peltier cooler. When present,thermal sink 230 provides several advantages. One such advantage is toprovide a reference temperature to which all portions of puck 200 willhave, in the absence of heat provided by heaters 220. That is, althoughheaters 220 can provide heat, such heat would ordinarily propagate, inall directions, throughout puck 200. Thermal sink 230 provides theability to drive puck 200 to lower temperatures, such that if a heater220 is located at a specific portion of puck 200, the heat generated bythe heater does not simply diffuse throughout puck 200 in everydirection, but heats a portion of puck 200 where the heat from theheater 220 locally exceeds the tendency of thermal sink 230 to removethe heat.

A related advantage is that thermal sink 230 can provide rapid thermalsinking capability such that when temperature settings of heaters 220(e.g., current passing through resistive wires) decrease, adjacentportions of puck 200 respond with a relatively rapid temperaturedecrease. This provides the benefit of being able, for example, to loadworkpiece 50 onto puck 200, provide heat through heaters 220, andachieve rapid stabilization of temperatures on workpiece 50 so thatprocessing can begin quickly, to maximize system throughput. Withoutthermal communication allowing some heat to dissipate to thermal sink230, temperatures reached by portions of puck 200 would decrease only asfast as other heat dissipation paths would allow.

In embodiments, heaters 220 are typically disposed in direct thermalcommunication with puck 200, while thermal sink 230 is in indirectthermal communication with puck 200, through heaters 220. It isadvantageous that thermal sink 230 not be in direct thermalcommunication with puck 200, because such direct thermal communicationcan lead to thermal anomalies on the surface of puck 200 (e.g., puck 200would have regions where temperature becomes close to the temperature ofthermal sink 230, instead of being dominated by extra heat generated byheaters 220). Also, heaters 220 have sufficient heat generationcapability that heat applied by heaters 220 can overwhelm the indirectthermal coupling of puck 200 with thermal sink 230, so that heaters 220can raise the temperature of inner portion 212 and outer portion 214 ofpuck 200, even while some of the heat generated by heaters 200dissipates into thermal sink 230. Thus, heat provided by heaters 220can, but does not immediately, dissipate through thermal sink 230. Inembodiments, degrees of thermal coupling among puck 200, heaters 220 andthermal sink 230 may be adjusted according to principles herein, inorder to balance considerations such as temperature uniformity withineach of the center and edge portions, rapidity of thermal stabilization,manufacturing complexity and cost, and overall energy consumption.

Yet another advantage of thermal sink 230 is to confine heat generatedby heaters 220 to the vicinity of puck 200. That is, thermal sink 230can provide a thermal upper limit for adjacent system components toprotect such components from high temperatures generated at puck 200.This may improve mechanical stability of the system and/or preventdamage to temperature sensitive components.

Heaters 220 and thermal sink 230 may be implemented in various ways. Inan embodiment, heaters 220 include several layers coupled together assubassemblies, which can then be further coupled with a 200 and(optionally) thermal sink 230 to form a wafer chuck assembly.Embodiments designed, assembled and operated as disclosed herein allowexplicit temperature control of workpiece (e.g., wafer) edge regionsrelative to center regions, and facilitate processing with explicitcenter to edge temperature control that is typically not achievable withprior art systems.

FIG. 4 is a schematic cross-sectional view of a portion of a waferchuck, that illustrates features of puck 200, a resistive heater actingas heater 220-1, and thermal sink 230. FIG. 4 represents a portion of awafer chuck that is near a cylindrical axis Z thereof, and is not drawnto scale, for illustrative clarity of smaller features. Puck 200 istypically formed of an aluminum alloy, for example of the well-known“6061” alloy type. Puck 200 is shown as defining surface grooves orchannels 205 that connect on upper surface 202 of puck 200, and withcentral channel 201 that is centered about axis Z. Vacuum may besupplied to central channel 201, reducing pressure within channels 205so that atmospheric pressure (or gas pressure of relatively highpressure plasmas, or low pressure deposition systems, such as around10-20 Torr) will urge workpiece 50 (see FIGS. 1, 2) against puck 200,providing good thermal communication between puck 200 and workpiece 50.

Inner resistive heater 220-1 is illustrated in FIG. 4, but it should beunderstood that the illustration and following description of innerresistive heater 220-1 apply equally to outer resistive heater 220-2.Resistive heater 220-1 includes a heater trace 264 and a buffer layer266. Heater trace 264 is shown as a continuous layer in FIG. 4, but isunderstood to exist as a layer that forms a serpentine pattern, todistribute heat evenly along its length (that is, heater trace 264 fallsalong the cross-sectional plane shown in FIG. 4, but in othercross-sectional views, would appear intermittently cross thecross-sectional plane—see FIG. 5). Heater trace 264 may be formed, forexample of Inconel of about 0.0005″ to 0.005″ thickness, although layersof about 0.0002″ to 0.02″ are also useful, as are other materialchoices. Buffer layer 266 is typically a polymer layer of about 0.025″to 0.10″ thickness, although layers of about 0.01″ to 0.15″ are alsouseful. Buffer layer 266 may be formed of polyimide, but other polymersand other material choices may be useful. Buffer layer 266 isadvantageously an electrical insulator (to avoid shorting heater trace264) that is thermally stable. Buffer layer 266 is also advantageouslycompressible, such that when coupled with a heater trace 264 that ismuch thinner, an opposing surface of buffer layer 266 is approximatelyplanar for mechanical purposes. Also, buffer layer 266 increases thermalresistance between heater trace layer 264 and thermal sink 230, so thatwhen heater trace layer 264 supplies heat, more of the heat transfers topuck 200 than to thermal sink 230.

In embodiments, heater trace layer 264 and buffer layer 266 are coupledwithin thin metal layers 260, 268 that help spread heat from heatertrace layer 264 evenly across surfaces of heater 220-1. A thin,electrically insulating layer 262 is included to keep metal layer 260from shorting heater trace layer 264; insulating layer 262 or insulatinglayer 266 may also act as a substrate for fabrication of heater tracelayer 264 (see FIG. 5). Insulating layer 262 is advantageously athermally stable material, may be formed of ceramic or a polymer such aspolyimide, and in embodiments has a thickness of about 0.001″ to 0.040″.Metal layers 260, 268 may be, for example, layers of Al 6061 of about0.005″ to 0.050″. Metal layers 260, 268 also provide moderate protectionfor layers 262, 264 and 266, so that heater 220-1 can be fabricated andshipped as a subassembly for later integration with puck 200 and thermalsink 230. For example, layers 260, 262, 264, 266, 268 and 270 that areshaped to the desired dimensions may be aligned into a stack inregistration with one another, and bonded by compressing and/or heatingthe stack, to form heater 220-1 as a subassembly. It will be evident toone skilled in the art upon reading and understanding the abovedisclosure, that heater subassemblies as disclosed herein will beroughly planar, and for wafer chuck applications will be roughlycircular, but similarly fabricated subassemblies need not be circular,and could be fabricated to fit differently shaped surfaces (e.g.,squares, rectangles, etc.) than the circular bottom surfaces ofcylindrical pucks described herein. Similarly, although heater tracesfor cylindrical pucks may be arranged for azimuthal uniformity anduniform heating density, heater traces within such subassemblies couldbe arranged to form locally intense and less intense heating patterns.

Heater 220-1 couples with puck 200 via an optional layer 250, and withthermal sink 230 via further optional layer 270, as shown. Layers 250and 270 promote thermal transfer between heater 220-1 and both puck 200and thermal sink 230; material choices of layers 250 and 270 includethermally stable polymers. In an embodiment, optional layers 250, 270are formed of layer of polymer having a bulk thermal conductivity ofabout 0.22 W/(m-K). Layers 250 and/or 270 may also be bondable to puck200 and layer 260, and thermal sink 230 and layer 268 respectively, suchthat puck 200, thermal sink 230 may be bonded together with heaters220-1 and 220-1. To accomplish this, puck 200, layer 250, heaters 220-1and 220-2, layer 270 and thermal sink 230 may all be aligned inregistration with one another, and bonded by compressing and/or heating.

In embodiments, thermal sink 230 provides a reference temperature forpuck 200, while still allowing inner and outer resistive heaters 220-1and 220-2 to provide center-to-edge temperature control for puck 200.Temperature of optional thermal sink 230 may be actively controlled. Forexample, FIG. 4 shows thermal sink 230 defining fluid channels 280through which a heat exchange fluid may be forced. Thermal sink 230 mayalso form thermal fins 290 to increase contact area and thus heatexchange efficiency of fluids within channels 280. Herein, “heatexchange fluid” does not require that the mixture always cool thermalsink 230; the heat exchange fluid could either add or take away heat.The heat exchange fluid may be provided at a controlled temperature. Inone embodiment, thermal sink 230 is formed of an aluminum alloy, such asthe “6061” type, and the heat exchange fluid is a mix of 50% ethyleneglycol and 50% water, although other materials may be used for thermalsink 230 and/or a heat exchange fluid. In still other embodiments,optional thermal sink 230 may be a passive thermal sink, e.g., thermalsink 230 may be a passive radiator, and may have heat fins and the like,to dissipate heat to a surrounding environment.

FIG. 5 schematically illustrates a layout of heater trace 264 oninsulating layer 262. The exact layout of heater trace 264 is notcritical, but it is desirable that the layout be dense and azimuthallyuniform. Heater trace 264 may terminate in a pair of bonding pads 274,as shown, for later connection with wires that deliver electrical power.As shown in FIG. 5, heater trace 264 need not extend into a centralregion 269 of inner resistive heater 220-1. One reason for this is thatthe temperature reached within puck 200 in the area surrounding region269 will rapidly spread across a corresponding region of puck 200.Another reason is that it may be desirable to leave region 269 open forother uses, such as to provide vacuum channel 201 (see FIGS. 3, 4),fluid connections for a heat exchange fluid, electrical contacts forheater trace 264, and/or other features.

A further advantage of providing at least one thermal break 210 thatintersects a top surface of puck 200 is that mechanical features may bedisposed at least partially within the thermal break such that thefeatures do not generate a thermal anomaly. For example, a wafer chuckcommonly provides lift pins that can be used to raise a wafer to a smalldistance off of the chuck to facilitate access by wafer handling tools(typically using a paddle or other device that, after the wafer israised, is inserted between the wafer and the chuck). However, the liftpins typically retract into holes in the chuck, and such holes canlocally affect wafer temperature during processing. When a thermal breakintersects a top surface of puck 200, a location already exists for sucha mechanism to be placed without introducing a thermal anomaly.

FIG. 6 schematically illustrates a portion of a wafer chuck that has alift pin mechanism 300 that controls a lift pin 310, disposed within athermal break 210. Portions of heaters 220 and optional thermal sink 230are also shown. The cross-sectional plane illustrated in FIG. 6 passesthrough a center of mechanism 300 such that the components thereof arewithin a lower portion of one thermal break 210. In and out of the planeshown, puck 200, thermal break 210 and thermal sink 230 may haveprofiles like those shown in FIGS. 3 and 4, so that the thermal break210 in which mechanism 300 is disposed will continue along its arcthrough puck 200 (see FIG. 7). Also, lift pin mechanism 300 is limitedto a fairly small azimuthal angle relative to the central axis of puck200 (again, see FIG. 7). That is, if a cross sectional plane were takenat a distance into or out of the plane shown in FIG. 6, the bottomsurface of puck 200 would be continuous along the same plane wherebottom surface 204 is indicated in FIG. 6, and thermal sink 230 would becontinuous under puck 200. The small size of lift pin mechanism 300limits thermal deviation of puck 200 in the area of lift pin mechanism300. FIG. 6 shows lift pin 310 in a retracted position, wherein it willnot create a thermal anomaly on the surface of puck 200.

FIG. 7 schematically illustrates, in a plan view, a three lift pinarrangement where lift pins 310 are disposed within a thermal break 210.FIG. 7 is not drawn to scale, in particular, thermal break 210 isexaggerated so as to show lift pin mechanisms 300 and lift pins 310clearly. Because lift pins 310 retract well below the average surface ofpuck 200 into thermal break 210, lift pins 310 do not generate a spatialthermal anomaly during processing, such that portions of a workpiecebeing processed at the locations of lift pins 310 (e.g., specificintegrated circuits located at the corresponding locations of asemiconductor wafer) experience processing that is consistent withprocessing elsewhere on the workpiece.

FIG. 8 is a flowchart of a method 400 for processing a wafer or otherworkpiece (simply called a “product wafer” hereinafter for convenience,understanding that the concepts may apply to workpieces other thanwafers). Method 400 may be uniquely enabled by the thermal managementapparatus described in connection with FIGS. 2-8 that can be used toprovide explicit center-to-edge thermal control, which in turn enablesexplicit center-to-edge process control. A first step 420 of method 400processes the product wafer with a first center-to-edge processvariation. A second step 440 of method 400 processes the product waferwith a second center-to-edge process variation that compensates for thefirst center-to-edge variation. Typically, one or the other of 420 or440 will be carried out in equipment or in a process environment thatunintentionally or uncontrollably generates the associatedcenter-to-edge process variation (the “uncontrolled variation”hereinafter) but this is not required. Also, typically, the other iscarried out in equipment such as that described herein, such thatanother center-to-edge process variation (the “controlled variation”hereinafter) is introduced through thermal management techniques thatallow the center and edge portions of the product wafer to be explicitlycontrolled to provide a corresponding, inverse process variation.However, the uncontrolled variation and the controlled variation canoccur in either order. That is, 420 may introduce either theuncontrolled or the controlled variation, and 440 may introduce theother of the uncontrolled and the controlled variation. FIGS. 9 and 10provide additional guidance to those skilled in the art to enable usefulexercise of method 400.

FIG. 9 is a flowchart of a method 401 that includes, but is not limitedto, step 420 of method 400. All of 410-418 and 422 shown in FIG. 9 areconsidered optional, but in embodiments may be helpful, in execution ofmethod 400 to achieve useful wafer processing results.

Step 410 sets up equipment characteristics that are related to the firstcenter-to-edge process variation, which will be produced at 420. Forexample, when 420 is expected to introduce the controlled variation, 410may involve providing equipment parameters such as heater settings thatwill provide a controlled center-to-edge temperature variation.Equipment such as described in FIGS. 2-7 herein is useful in providing acontrolled center-to-edge temperature variation. Step 412 measuresequipment characteristics that are related to the first center-to-edgeprocess variation. Process knowledge may be acquired over time aboutwhat equipment settings, or measured equipment characteristics, aresuccessful in generating a known center-to-edge process variation (or atleast providing a process variation that is stable, albeitunintentional). In consideration of this process knowledge, method 401may optionally return from 412 to 410 to adjust equipmentcharacteristics, if the equipment characteristics measured in 412 canlikely be improved. Step 414 processes one or more test wafers thatreceive the first center-to-edge process variation. Step 416 measuresone or more characteristics of the first center-to-edge processvariation on the test wafer(s) processed in step 414. Method 401 mayoptionally return from 416 to 410 to adjust equipment characteristics inlight of the center-to-edge process characteristics measured in 416. Anytest wafers processed in 414 may optionally be saved in 418, for testingin the second process (e.g., the process to be executed later, in 440).Also, 414 may be performed in parallel with 420. That is, when processequipment is appropriately configured, test wafers may be processed atthe same time as product wafers (for example, if the first process is aso-called “batch” process like dipping a cassette of wafers into aliquid bath, processing a set of wafers together in an ampoule,diffusion furnace or deposition chamber, or the like).

Step 420 processes a product wafer with the first center-to-edge processvariation. Step 422 measures one or more first center-to-edgecharacteristics on the product wafer, to generate data for equipmentprocess control purposes, for correlation to yield or performance of theproduct wafer, and/or for use in correlating to information surroundingstep 440, as described further below.

FIG. 10 is a flowchart of a method 402 that includes, but is not limitedto, step 440 of method 400. All of 430-436 and 442 shown in FIG. 10 areconsidered optional, but in embodiments may be helpful, in execution ofmethod 400 to achieve useful wafer processing results.

Step 430 sets up equipment characteristics that are related to thesecond center-to-edge process variation, which will be produced at step440. For example, when 440 is expected to introduce the controlledvariation, 430 may involve providing equipment parameters such as heatersettings that will provide a controlled center-to-edge temperaturevariation. Equipment such as described in FIGS. 2-7 herein is useful inproviding a controlled center-to-edge temperature variation. Step 432measures equipment characteristics that are related to the secondcenter-to-edge process variation. In consideration of process knowledge,as discussed above, method 402 may optionally return from 432 to 430 toadjust equipment characteristics in light of the equipmentcharacteristics measured in 432. Step 434 processes one or more testwafers that receive the second center-to-edge process variation; thetest wafer(s) processed in 434 may include one or more test wafers savedfrom the first process step in 418, above. Step 436 measures one or morecharacteristics of the second center-to-edge process variation on thetest wafer(s) processed in 434. In consideration of previously acquiredprocess knowledge, method 402 may optionally return from 436 to 430 toadjust equipment characteristics in light of the center-to-edge processcharacteristics measured in 436.

Step 440 processes a product wafer with the second center-to-edgeprocess variation. Also, although not shown in method 402, additionaltest wafers could certainly be processed in parallel with the productwafer. Step 442 measures one or more first center-to-edgecharacteristics on the product wafer, to generate data for equipmentprocess control purposes, for correlation to yield or performance of theproduct wafer, and/or for use in correlating to information surrounding420, as described above. Such measurements could also be performed onany test wafer that was processed in parallel with the product wafer,but in any case 442 will generally not further alter any conditionpresent on the product wafer. That is, the results of 420 and 440 willbe fixed in the product wafer at the conclusion of 440 irrespective ofany further testing done.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Processing of workpieces other than wafers may also benefit fromimproved processing uniformity, and are considered within the scope ofthe present disclosure. Thus, characterization of the chucks herein as“wafer chucks” for holding “wafers” should be understood as equivalentto chucks for holding workpieces of any sort, and “wafer processingsystems” as similarly equivalent to processing systems.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the electrode” includesreference to one or more electrodes and equivalents thereof known tothose skilled in the art, and so forth. Also, the words “comprise,”“comprising,” “include,” “including,” and “includes” when used in thisspecification and in the following claims are intended to specify thepresence of stated features, integers, components, or steps, but they donot preclude the presence or addition of one or more other features,integers, components, steps, acts, or groups.

We claim:
 1. A workpiece holder that positions a workpiece forprocessing, the workpiece holder comprising: a substantially cylindricalpuck that is characterized by a cylindrical axis, a puck radius aboutthe cylindrical axis, and a puck thickness, wherein the puck radius isat least four times the puck thickness, wherein at least a top surfaceof the cylindrical puck is substantially planar, and wherein thecylindrical puck defines one or more radial thermal breaks, each thermalbreak being characterized as a radial recess that intersects at leastone of the top surface and a bottom surface of the cylindrical puck,wherein the radial recess is characterized by: a thermal break depththat extends from the top surface or the bottom surface of the puckthrough at least half of the puck thickness, and a thermal break radiusthat is disposed symmetrically about the cylindrical axis, and is atleast one-half of the puck radius; and wherein the radial recessintersects the top surface, the workpiece holder further comprising atleast three lifting elements that extend above the top surface in anextended state, to lift the workpiece from the top surface, and thatretract into the radial recess in a retracted state, to lower theworkpiece onto the top surface.
 2. The workpiece holder of claim 1,further comprising: a first heating device disposed adjacent to thebottom surface of the puck and radially inward from the one or morethermal breaks relative to the cylindrical axis, the first heatingdevice being in thermal contact with the bottom surface of the puckwithin the thermal break radius, and a second heating device disposedadjacent to the bottom surface of the puck and radially outward from theone or more thermal breaks relative to the cylindrical axis, the secondheating device being in thermal contact with the bottom surface of thepuck outside the thermal break radius.
 3. The workpiece holder of claim2, wherein at least one of the first and second heating devicescomprises a heater element trace that is disposed within a plurality ofelectrically insulating layers.
 4. A workpiece holder that positions aworkpiece for processing, the workpiece holder comprising: asubstantially cylindrical puck that is characterized by a cylindricalaxis, a puck radius about the cylindrical axis, and a puck thickness,wherein: the puck radius is at least four times the puck thickness, atleast a top surface of the cylindrical puck is substantially planar, andthe cylindrical puck defines one or more radial thermal breaks, eachthermal break being characterized as a radial recess that intersects atleast one of the top surface and a bottom surface of the cylindricalpuck, wherein the radial recess is characterized by: a thermal breakdepth that extends from the top surface or the bottom surface of thepuck through at least half of the puck thickness, and a thermal breakradius that is disposed symmetrically about the cylindrical axis, and isat least one-half of the puck radius; a first heating device disposedadjacent to the bottom surface of the puck and radially inward from theone or more thermal breaks relative to the cylindrical axis, the firstheating device being in thermal contact with the bottom surface of thepuck within the thermal break radius; and a second heating devicedisposed adjacent to the bottom surface of the puck and radially outwardfrom the one or more thermal breaks relative to the cylindrical axis,the second heating device being in thermal contact with the bottomsurface of the puck outside the thermal break radius; wherein: at leastone of the first and second heating devices comprises a heater elementtrace that is disposed within a plurality of electrically insulatinglayers, the heater element trace comprises a resistive material, and atleast one of the electrically insulating layers comprises polyimide. 5.The workpiece holder of claim 4, wherein the radial recess ischaracterized by a thermal break radius that is at least 60% of the puckradius.
 6. The workpiece holder of claim 4, wherein the heater elementtrace and the electrically insulating layers are disposed within aplurality of metal layers.
 7. A workpiece holder that positions aworkpiece for processing, the workpiece holder comprising: asubstantially cylindrical puck that is characterized by a cylindricalaxis, a puck radius about the cylindrical axis, and a puck thickness,wherein: the puck radius is at least four times the puck thickness, atleast a top surface of the cylindrical puck is substantially planar, andthe cylindrical puck defines one or more radial thermal breaks, eachthermal break being characterized as a radial recess that intersects atleast one of the top surface and a bottom surface of the cylindricalpuck, wherein the radial recess is characterized by: a thermal breakdepth that extends from the top surface or the bottom surface of thepuck through at least half of the puck thickness, and a thermal breakradius that is disposed symmetrically about the cylindrical axis, and isat least one-half of the puck radius; a first heating device disposedadjacent to the bottom surface of the puck and radially inward from theone or more thermal breaks relative to the cylindrical axis, the firstheating device being in thermal contact with the bottom surface of thepuck within the thermal break radius; a second heating device disposedadjacent to the bottom surface of the puck and radially outward from theone or more thermal breaks relative to the cylindrical axis, the secondheating device being in thermal contact with the bottom surface of thepuck outside the thermal break radius; and a thermal sink that extendssubstantially across the bottom surface of the cylindrical puck, thefirst and second heating devices being disposed between the thermal sinkand the bottom surface of the cylindrical puck.
 8. The workpiece holderof claim 7, wherein the thermal sink comprises a metal plate thatdefines one or more fluid channels.
 9. The workpiece holder of claim 7,wherein: the first and second heating devices comprise respective firstand second heater element traces that are disposed between first andsecond electrically insulating layers; the first electrically insulatinglayer is disposed between the first and second heater element traces andthe thermal sink; the second electrically insulating layer is disposedbetween the first and second heater element traces and the bottomsurface of the cylindrical puck; and the first electrically insulatinglayer is thicker than the second electrically insulating layer, suchthat the first electrically insulating layer increases thermalresistance between the heater element traces and the thermal sink sothat when the heater element traces supply heat, more of the heattransfers to the puck than to the thermal sink.
 10. The workpiece holderof claim 9, wherein the first one of the electrically insulating layerscomprises ceramic.
 11. The workpiece holder of claim 9, furthercomprising: first and second metal layers; and first and secondthermally stable polymer layers; and wherein the workpiece holder isbonded together, with the elements and layers disposed in the followingphysical order from bottom to top: the thermal sink; the first thermallystable polymer layer; the first metal layer; the first electricallyinsulating layer; the first and second heater element traces at the samelevel, the second heater element trace being radially outward from thefirst heater element trace; the second electrically insulating layer;the second metal layer; the second thermally stable polymer layer; andthe puck.
 12. The workpiece holder of claim 7, wherein the cylindricalpuck defines two of the radial thermal breaks; a first one of the radialthermal breaks being characterized as a radial recess that intersectsthe top surface of the cylindrical puck, the thermal break depth of thefirst one of the radial thermal breaks extending downwardly from the topsurface of the puck through more than half of the puck thickness; and asecond one of the radial thermal breaks being characterized as a radialrecess that intersects the bottom surface of the cylindrical puck, thethermal break depth of the second one of the radial thermal breaksextending upwardly from the bottom surface of the puck through more thanhalf of the puck thickness.
 13. A workpiece holder that positions aworkpiece for processing, the workpiece holder comprising: asubstantially cylindrical puck that is characterized by a cylindricalaxis and a substantially planar top surface, wherein the cylindricalpuck defines two radial thermal breaks, a first one of the thermalbreaks being characterized as a radial recess that intersects a bottomsurface of the cylindrical puck at a first radius, and extends from thebottom surface through at least one-half of a thickness of the puck; asecond one of the thermal breaks being characterized as a radial recessthat intersects the top surface at a second radius that is greater thanthe first radius, and extends from the top surface through at leastone-half of the thickness of the puck; a thermal sink that extendssubstantially beneath the bottom surface of the puck, the thermal sinkcomprising a metal plate that flows a heat exchange fluid throughchannels defined therein, to maintain a reference temperature for thepuck; a first heating device disposed between the thermal sink and thepuck, the first heating device being in thermal communication with thebottom surface of the puck and with the thermal sink, within the firstradius; and a second heating device disposed between the thermal sinkand the puck, the second heating device being in thermal communicationwith the bottom surface of the puck and with the thermal sink, outsidethe second radius.
 14. The workpiece holder of claim 13, wherein: thefirst and second heating devices comprise respective first and secondheater element traces that are disposed between first and secondelectrically insulating layers.
 15. The workpiece holder of claim 14,wherein: the first electrically insulating layer is disposed between thefirst and second heater element traces and the thermal sink; the secondelectrically insulating layer is disposed between the first and secondheater element traces and the bottom surface of the cylindrical puck;and the first electrically insulating layer is thicker than the secondelectrically insulating layer, such that the first electricallyinsulating layer increases thermal resistance between the heater elementtraces and the thermal sink so that when the heater element tracessupply heat, more of the heat transfers to the puck than to the thermalsink.
 16. The workpiece holder of claim 14, wherein the first one of theelectrically insulating layers comprises ceramic.
 17. The workpieceholder of claim 14, further comprising: first and second metal layers;and first and second thermally stable polymer layers; and wherein theworkpiece holder is bonded together, with the elements and layersdisposed in the following physical order from bottom to top: the thermalsink; the first thermally stable polymer layer; the first metal layer;the first electrically insulating layer; the first and second heaterelement traces at the same level, the second heater element trace beingradially outward from the first heater element trace; the secondelectrically insulating layer; the second metal layer; the secondthermally stable polymer layer; and the puck.